Variable stroke radial pump



Patented Aug. 18, 1942 i 2,293,692 VARIABLE STROKE RADIAL PUMP Hamilton Neil Wylie, London, England, assignor to Aircraft Hydraulic Appliances Limited,

London, England Application ct0ber 13, 1939,` Serial No. 299,347

In Great Britain October 26, 1938 21 Claims. (Cl. 10S-161) The invention relates to variable -stroke radial pumps. There is a known and used kind of pump, which broadly speaking comprises a relatively rotating cylinder assembly with cylinders directed radially or substantially radially, and pistons in the cylinders which are constrained to reciprocate therein by a, track ring, usually of diametrically opposite.

circular form. The track ring is movable bewith reference to the axis of rotation of the cylinder assembly or between concentric and v eccentric positions, so that the stroke of the piston is variable and the rate of delivery of the pump for givenrunning speeds, is variable. 'I'he track ring is loaded towards an eccentric position by controlling means in opposition to which uid pressure produced in the cylinder assembly in operation of the pump against pressure acts to reduce eccentricity of the track ring, thereby reducing the eiective stroke of the pistons and, correspondingly, the output. It is to pumps of that kind, that the present invention relates, whether the variation is manual or automatic. The present invention consists in a radial pump of the kind stated which is variable in stroke by,the track ring moving to vary its eccentricity in a path in the plane of rotation of the cylinder assembly, in which valve means which determine the direction of total reaction of the piston and cylinder assembly on the track ring and disposed, when the pump is operating against pressure, with a bias such that this direction, for all positions of the track ring, is such as to produce a component of force in the direction of the said path tending to reduce the eccentricity against the force exerted by the controlling means.

The control system' of this invention is described with particularity with regard a radial pump, however, there are many types of variable delivery pumps upon which the control system of this invention maybe applied. Many of the variable delivery pumps are controlled automatically to vary theirdelivery rate, which pumps have included large and cumbersome control devices for automatically controlling the rate of delivery. All of these former, produce various reaction forces, which if controlled in accordance with the teachings of this invention, will permit 'more sensitive automatic control over the' delivery rate.

The bias introduced by the valve means is due to the collective pressure eect of the rotating cylinder and plunger assembly and it will be appreciated that when the ring is eccentric the plungersI when approaching the point of the ring which is nearest to the centre4 of the cylinder vassembly are making a positive stroke and when this point is passed in rotation .the plungers are making the return stroke; hence that point is on dead centre and the other dead centre is If the cylinders Ware open to the pressure duct exactly on the dead centre at the start of the'pressure vstroke and were to close on the Opposite dead centre, the average pressure exerted lon the ring by the plungers would be zero in a direction parallel to the diameter containing the dead centres. By delaying the release of pressure from the plungers on that side of the ring which is nearest the centre of the cylinder assembly and also by delaying the point at which the plungers on the opposite side of the assembly are opened to pressure, the average )pressure due to the plungers pressing on the ring is given a bias which opposes the action of the spring and tends to decrease the eccentricity. For opening the cylinders to inlet and exhaust it is convenient to provide lands on a valve member about which the cylinder assembly rotates, the lands dening in eiect peripheral grooves on opposite sides of the valve, one in communication with an inlet duct and the other in communication with an outlet duct. Thus it follows that the bias eiect can be produced by extending one end of a groove beyond the dead centre and/or by shortening the duct atthe other end. The same bias effect would be produced by rotating the valve through an angle in the direction of rotation of the cyl- -inder assembly and the angle through which the valve is thus rotated would again be the angle of bias of the valve.

One feature of the present invention consists in the provision of a radial pump of the kind stated, which is variable in stroke by the track ring moving to vary its eccentricity in a constrainedl path in the direction of the plane of rotationlof the cylinder assembly, in which valve means, which determine the direction of total reaction on the track ring, are disposed with a bias such that this direction, for all positions of the vtrack ring, Vis such as to produce a component of force in the direction of the said path and therefore tending to` change the eccentricity; and means for controlling the moving of the track ring are provided, adapted and proportioned to resist said component of force. In all cases the said component is in itself a force of substantially less magnitude than the total reaction, so that. the means for controlling can themselves be made less in size and weight than 'if they had to resist the total reaction, and it is believed, less complicated, and more effective than if they were meeting no reaction but merely causing the movements of the track ring along a path to'which the reaction was at right-angles. Preferably, the component resisted by the controlling means in a minor component, of the order of about one-tenth of the value of the total reaction, and the means which resists it may comprise a spring so arranged that the controlling resistance to the component above mentioned, is resilient over the whole range of movement of the track ring in such a manner that the variations of stroke (and therefore of delivery rate) of the pump are rendered automatically dependent on the pressure generated. As will be seen hereafter, a particular kind of spring and arrangement thereof is preferably employed as the controlling means, thus not only resulting in a convenient and compact arrangement, but also one in which a certain relationship between delivery pressure and delivery rate is obtained, which relationship may be uniform or non-uniform over the range of operation.

It follows thatl an arrangement according to the present invention provides a pump of simple, light, compact and durable construction such as will be particularly suited for duty as a continuously engine-driven hydraulic pump in an air pressure rise in the receiver or system againstwhich the pump is operating, so that there is thus in practice a critical maximum delivery pressure within which the delivery rate falls off to zero or to such small value as might be desirable to make up for leakage losses in a supplied system or in the pump itself.

A further main feature of the invention relates to the manner of constraint of the track ring by virtue of which frictionmay largely be avoided, the major component of reaction can be very conveniently met, and other practical advantages are achieved. This feature residesin the provision that, in a radial variable 'stroke pump of the kind stated, the track ring is pivotally supported for angular movement to vary the stroke of the pump. The usual arrangement of a track ring mounted slidably between constraining guides is therefore avoided. The valve bias which determines the direction of the total reaction previously mentioned, is preferably arranged so that this direction is 'offset from the axis of angular movement of the track ring, so `that the total reaction has a moment about the axis, and thus sets up the previously mentioned component of force, as a force tangential to an arc in which the track ring moves, tending to decrease eccentricity of the track ring relative to the cylinder assembly with which the said valve co-operates. Preferably the valve is a hollow spindle-like element about which the cylinder assembly rotates, ports and passages coming successively into communication between the cylinders and the valve. The invention includes further details relating, for` example, to the fact that the valve element is variably settable to relationships between the track ring and the casing; and tothe particular choice of spring and its arrangement in the casing; and certain other constructional details.

The cylinder assembly and the track ring are preferably mounted within a stationary casing, and the track ring is pivotally supported in the casing and may be slidingly supported by a wall or wall part opposite to the swing axis and formed arcuately from the axis about which the ring swings. A certain kind of spring, based on the principle of the Euler strut, is preferably employed for the automatic control of eccentricity by balancing the moment due to the total reaction of the pressure loaded pistons, and this takes the form of a bowed resilient strut, mounted between the track ring and casing, and bowed in such direction that its curvature corresponds with that of the ring and internal Wall of the casing. This results in a very compact arrangement and also one in which the moment of the spring about the swing axis of the ring can be selected critically. The invention also includes certain constructional features which may be embodied in conjunction with the broader'features above mentioned, as set out in the claims and as more fully described with reference to the accompanying drawings. These drawings comprise:

Figure 1, which is an axial, partly sectional, elevation of the pump, and

Figure 2, which is a partly sectional elevation at right angles to Figure 1.

Figure 3 is a sectional elevation taken through an end cover plate of the pump body to show the arrangement of certain ports not apparent from Figures 1 and 2. v

Figure 4 is a graph indicating the relation of delivery to pressure encountered at the output.

The pump illustrated is intended for liquids and has two stages: the first, a non-positive lowpressure stage achievedV by centrifuging Within the casing, the second a high-pressure positive stage using pistons and cylinders. The first stage is arranged to have, within operative speeds, an output which will always exceed that of the second, and which consequently injects liquid to the second stage. Moreover, assuming the liquid to be lubricatingin quality, the whole of the high-speed friction surfaces are thus lubricated and the Working parts are kept ooded and cooled.

An outer casing I has an internal formation which affords a diffuser or outlet channel at IA for the centrifugal liquid to emerge from the interior of the casing. The inwardly facing concave wall of the casing supports a pivot roller or pin provided with an axis 3, which in turn pivotally supports the track ring 2.,-' The wall, opposite the locality of the pin at 3, is arcuate at ID and centred on the axis 3. Y The slideway formed by the arcuate wall part is bounded at each extremity by wall-formations at IB, IC, which form abutment surfaces limiting the movement of the ring 2 in swinging on the axis 3. The track ring 2 is channel-sectioned, and in the channel a clear path is provided for the crowns of pistons. side-flanges 2B of the track ring form the actual tracks, and the track ring therefore encloses the plunger and cylinder asembly except for the port 2C (Figure 1) through which liquid passes centrifugally into the diffuser IA. In Figure 1 the The inner edges 2A of the track ring is shown in the limit position correv sponding to no delivery, i. e., it is concentric with the rotating cylinder assembly. In this position a track ring controlling loading spring is fully distorted; this is the Euler-strut laminated leaf spring 4, which is lodged between an abutment 5 in the casing I and an abutment 6 on the outside of the track ring 2. The spring 4 is so dimensioned that it is always bowed to some curvature even at full eccentricity of the ring and though in theory a Euler strut spring has no rate, the spring 4 is in fact, contrived so as to depart slightly from this condition of rate, so as to have in fact a small rate.` It has now been seen' that the track ring 2 can rock about the axis 3 between limits from its maximum eccentricity to its zero eccentricity against the resistance of the spring 4, which resistance increases slightly as the spring is progressively further bowed or deflected. It will be observed that the bowing of the spring 4 is arranged to conform with the general curvature of the space, between the ring 2 and casing I, in which it lies. A line 4A has been drawn between the abutments 5 and 6, representing the direction of force of the spring, and reference will be made to this line anon.

Into one side of the casing I in appropriate ball bearings IA and through a gland 1B extends-v the pump driving shaft l'IC which, within the casing I engages through the medium of an I Oldham coupling 26 a cylindrical sleeve I'I with which air integral the radially extending cylinders 8 which, in the example, are seven in number. Each cylinder 8 has a port 8A opening to the interior axial bore of the sleeve I'I. Fitting Within the sleeve I'I and extending thereinto from the other side of the casing I, is a non-rotating hollow axial valve 9 in which are formed an arcuate inlet groove I supplied by an axial bore IIlA and a similar arcuate output groove II connected tof'a second axial bore I IA in the valve 9. The bore IOA is connected by a duct IUB, formed in the side wall vof the casing I, to he outlet IA of the low-pressure stage. The dell ery or outlet duct IIA is of course connected to the desired receiver from the v"pump by a suitable union such as IIC. The duct IIA is connected through a spring-loaded relief valve IIB, back to the duct IDB, for relief of delivery pressure in the event of overload. Between the adjacent terminals of the grooves I8 and Il, are two arcuately profiled lands I2 and I3; the positions and dimensions of these lands are important: the land I2 must be long enough circumferentially completely to cut olf one port 8A, whilst the land I3 preferably subtends an even greater angle. The orientation orphase-position of these lands will be mentioned later.

In each cylinder 8 there is provided a piston I4; side loads on the plungers I4 are avoided in the following manner. Each plunger I4 abuts on a retaining piece 21 which is secured at I4A to a cylinder-like pot I which is a sliding t on the outside of the corresponding cylinder 8, and which engages with some clearance a circular groove in I4. The outer ends of the plungers Id and pots I5 run clear within the channel of the track ring 2 as previously mentioned. Each pot has a pair of arcuate recesses I5A formed in its wall (which is cut away for accommodation) in which mate rockably arcuate lugs IBA projecting from slippers I 6 which encircle the pots and which, having arcuate bearing surfaces, run on the track surfaces at 2A on each side of the pistons. The slippers are lapped to the tracks and are preferably so proportioned and formed as to operate as Michell pads and thus practically or wholly eliminate frictional contact. The pivot action afforded by the mating lugs IGA and their complementary recesses ISA permit the slippers I6 to rock relatively to the pots I5 so as to occommodate the varying eccentricity of the track ring.

The cylinders 8, pots I5 and slippers I6, which collectively constitute the cylinder assembly, form for the purposes of the first stage of the pump, a centrifugal rotor. Liquid being supplied for example by gravity through a conveniently arranged passage such as that indicated at IE (Figure 1), to= the interior of the casing I and assuming the shaft 1C and consequently the cyllnder assembly to be rotating anti-clockwise (Figure 1), liquid is centrifugally impelled out through the slot 2C into IA and thus creates a pressure head in IIIA through passage IOB andl` 'by the land I2, the incoming pistons I4 in the second half-cycle pump the liquid out through ports 8A, groove II and duct IIA. Each cylinder is then in turn cut oil* by land I2 to begin a fresh cycle. y

The delivery volume at/ a given'R. P. M. within the working range, by centrifugal action, is arranged to be greater than the through-put of the cylinders 8 at the same R. P, M. even at maximum stroke, and consequently the second stage of the pump is never able to cope with, the volume which reaches it so that, a relief by-pass is provided, for example through a somewhat constricted passageway 28; (alternatively a lightly loaded spring valve may be used as a restriction) to return surplus low-pressure `delivery to the reservoir or original source from the duct IDB or more directly from the diffuser at IA.

In Figure l a line X-X is drawn, intersecting the axis 3 and the axis of the valve 8, i. e., of rotation of the cylinder assembly and a line Y--Y passes through the rotation axis and is offset from axis 3. The position of the valve lands I2, I3, angularly, is of importance in this pump. The line Y-Y is intended to represent thedirection of the total reaction of the pistons on the track ring, i. e., the resultant of radial load due to fluid pressure reaction on the pistons and their centrifugal force,and that of their associated parts, tangential, friction of the slippers against the tracks, and the tangential component of .radial load due to eccentricity of the track with respect to the axis of gyration of the pistons. If the line Y-Y coincided with X-X, it is clear that the total reaction on the track ring would merely result in compression of the pivot bearing at 3. In fact, the angle to which Y--Y is offset is determined for given running conditions by the bias of the valve, i. e., the angular position of the valve lands, i. e., the cut-olf and opening positions of the ports.'v If the valve 8 were rotated further anti-clockwise, the line Y-Y would be displaced more anti-clockwise from X-X. Indeed, it is proposed to provide for angular setting of the valve for this reason. The immediate point is, however, that the angle which Y-Y makes with X-X determines the value of the moment of force which the reaction on the ring 2 has about the axis 3. This moment is that which is resisted by the spring 4 and as the moment arm is small, a very small increase in angle affords a considerable decrease in pressure. It is at once apparent that a very sensitive adjustment is afforded, between the output pressure of the pump (the main factor in the value of the reaction moment) and the stroke of the pump which is determined by the swinging of the ring 2 and therefore by the moment of the spring 4 about the axis 3, the direction of which is shown by line 4A. Now, the angle of the line 4A with reference to axis 3, changes as the track ring swings, in such a way that the length of the effective moment-arm of the spring 4 varies as the eccentricity varies and by selection of the position of abutment 5 and also of abutment 6 can be made to decrease or increase as the eccentricity decreases. Thus, whatever rate the spring I may naturally have is, in effect, decreased as eccentricity decreases. It can thus be arranged that the ratio between rate of delivery of the pump and increase of pressure has a critical value or a fairly critical value, beyond which the rate decreases rapidly for a relatively small further increase of pressure and the decrease in rate of delivery may even be accompanied by a decrease in pressure.

A typical relationship between delivery pressure and rate of delivery is illustrated with ref-- erence to Figure 4 showing the` delivery curve in respect of a pump driven at 280() R.. P. M. such as is likely to be employed for feeding a fluid pressure system of an aircraft and giving a maximum delivery rate of just over 31/2 gallons per minute at that driven speed. When operating the hydraulic services of theaircraft under many conditions the track ring is at maximum eccentricity, and remains so right up until the maximum output pressure is reached, in this case just about 1800 lbs. per square inch, whereafter there is a rapid falling off of output to the delivery rate of zero, or to just sufficient to make up for leakage and maintain the pressure at, in this case, about 1800 lbs. per square inch.

The falling off of delivery rate is dependent on the nature and/or the arrangement of the spring, and if a more gradual falling off were required the spring 4 could be formed with an initial bend before being further bent by compression between the stops, or the spring 4 might be replaced by a spring of another type, that is, a spiral spring.

The path of the track ring in angular movement is constrained by virtue of the mounting of the ring, so Athat the centre of the track ring swings in an arc which practically intersects the axis of rotation of the cylinder assembly. When the condition is reached, that practical concentrcity arises, there is practically zero delivery. However, a small eccentricity may be afforded such that leakage loss is made up when the pump is not delivering and this departure from exact concentricity is chosen so that the suction side of the pump has a slightly greater volumetric ca.- pacity than the pressure side.

It will also be understood that a majo1` component of the. reaction along Y-Y is resisted by the pivotal bearing at 3; in other words, a large proportion of the reaction due to pump pressure is transmitted directly to the casing I, which is well adapted to resist it. It is therefore advantageous to arrange that the bias angle of the line Y-Y should be quite small and angles of the order of 5 have been found to be satisfactory,

this giving a component force which is in the order of one-tenth of the total reaction.

The direct bearing pressure of the sleeve l1 on the valve 9 is substantially reduced by the fact that the fluid pressure in the groove ll of the valve 9 reacts on the sleeve Il in opposition to the pistons I4 which are under pressure.

The pots l5 may be held outwardly when the pump is idle, by one or more circular rings such as 15B, bearing on shoulders ISC of the pots.

What I claim is:

1. A radial pump of the kind specified comprising a cylinder assembly arranged for rotation, piston means reciprocable in the cylinders of said cylinder assembly, a track ring movable in a constrained path in the direction of the plane of rotation of said assembly to vary its eccentricity relative to said assembly so as to vary the stroke of the piston, track engaging means associated with said pistons and cooperating with said track ring to transmit to said piston means the reciprocation and stroke control exercised by said track ring, valve means determining the direction of total reaction on said track ring to produce a minor component of force in said direction to vary the eccentricity of Asaid track ring, and a bowed resilient strut having substantially no rate mounted in compression in operative engagement with said track ring to' apply substantial pressure thereon to resist movement thereof as caused by said component.

2. A radial pump of the kind specified, comprising a cylinder assembly arranged for rotation about a first axis, piston means reciprocable in the cylinders of said assembly, a track ring engaged by said pistons and pivotally supported for angular movement about a second axis substantially parallel with the first axis to vary the stroke of pistons of said assembly by variation of eccentricity, control means comprising a strut in substantially parallel relationship with respect to the periphery of said track ring having one end thereof-in engagement with the track ring and the opposite end thereof in engagement with a fixed abutment in said pump, said strut having substantially strong forceand substantially no rate to urge said track ring to full stroke and valve means having port passages cooperating with said assembly arranged angularly with respect to the track ring axis to determine the direction of total reaction on said track ring so that a component of said reaction has a minor moment about said second axis which is resisted by said control means to control the change of eccentricity of said track ring from maximum to minimum.

3. A pump according to claim 2, wherein the control strut means cooperates with 'said track ring to produce a decreasing moment about said second axis in the same plane as and in the opposite sense to the moment of said component.

4. A radial pump of the kind specified .comprising a stationary valve element, a cylinder assembly rotatable about a first axis' relatively to, and co-operating in such rotation with, said valve element, pistons in said assembly, a track ring engaged by said pistons and mounted for angular movement about a second axis parallel with and spaced from said first axis and spaced also from the centre of the ring, resilient means having a decreasing effect with decreasing eccentricity of said track ring to urge said'track ring angularly about said second axis, said valve element and said cylinder assembly being so arranged that the total reaction on said track ring` hasa component of force producing a small moment of increasing eiect about said second axis in opposition to said resilient means.

5. A radial pump of the kind specied comprising a casing, a cylinder assembly rotatable therein about a first axis, pistons in said assembly, a track ring engaged by saidpistons and mounted in said casing for angular movement about a second axis which is spaced from said first axis, valve means operative in the rotation of said assembly to govern the direction of total reaction between said assembly and said track ring and produce a minor moment about said second axis, and a bowed resilient strut mounted in compression between said casing and said track ring to produce a moment about said second axis in opposition to said rst mentioned moment, said second mentioned moment being reduced by a decreasing eccentricity of said track ring and said cylinder assembly.

6. A radial pump of the kind specied comprising a stationary valve element, a cylinder assembly rotatable about a first axis relatively to, and co-operating in such rotation with, said valve element, a track ring mounted for angular movement about a second axis parallel with and spaced from said rst axis, pistons reciprocably mounted in the cylinders of said assemblies and being in operative engagement with the track ring, resilient means to urge said track ring angularly about said second axis, and said valve element and said cylinder assembly being so arranged that the total reaction on said track ring has a component of force biased angularly about said first axis producing a moment about said second axis in opposition to said resilient means, said valve element having a high pressure groove, and a low pressure groove separated therefrom by lands, such lands being so disposed that the line through the center of the valve element and perpendicular to the line joining the edges of the lands which de-limit the high pressure groove is oiset from the said second axis.

7. A radial pump comprising, a casing, a track ring pivotally mounted within said casing, a cylinder assembly rotatable within said track ring about a fixed pintle, pistons in said assembly and engaging said track ring, said pintle having radial inlet and outlet ports therein arranged with respect the axis of rotation of the cylinder assembly and the track pivot, whereby the reaction forces of the pump produces a total reaction force biased about the pintle and displaced angularly from the track pivot, the major component thereof being carried by the track pivot the minor component causes shifting of the track about its pivot to vary the eccentricity thereof with respect the cylinder assembly, an arcuate spring positioned under compression between said track and said casing urging said track to the eccentric position thereof, said spring having a moment about the track pivot which decreases as theeccentricity of the track with respect the cylinder assembly decreases.

9. A radial pump of the kind speciied comprising a cylinderl and piston assembly arranged for rotation, a non-rotating tra-ck ring engaged by said pistons and movable in a constrained path in the plane of rotation of said assembly to vary its eccentricity relative to said assembly so as to vary the stroke of the pump, valve means `determining the direction of total reaction on said track ring as such, when the pump is operating against pressure, as to producea minor component of force in said direction, an arcuatestrut positioned in substantially parallel relationship with respect to the periphery of said track ring and having one end thereof in engagement with a fixed abutment and theopposite end in engagement with said track ring whereby said strut resists track ring movement caused by said component.

10. A radial pump of the kind specified, com-A prising a rotatable 'cylinder assembly, pistons for said assembly, a track ring engaged by said pistons and movable to vary vthe stroke of pistons ofthe strut is bowed in initial compression to exert a predetermined force by location between end stops.

l2. A radial pump of the kind specified comprising a casing, a cylinder assembly rotatable therein about a first axis, pistons for said assembly, a track ring engaged by said pistons, mounted in said casing for angular movement about a second axis which is spaced from said first axis and from its own centre, valve means having land areas operative in the rotation of said assembly to divide said assembly'into suction inlet and pressure discharge units and to govern the While the minor component causes shifting of I the track about its pivot to vary the eccentricity thereof with respect the cylinder assembly, and an arcuate strut having substantially no rate but a relatively large force in operative association withsaid track to urge same to eccentric position.

8. A radial pump comprising, a casing, a track ring pivotally 4mounted within said casing, a cylinder assembly rotatable within said track ring about a xed pintle, pistons in' said assembly and engaging said track ring, said pintle having radial inlet and outlet ports therein arranged with respect the axis of rotation of the cylinder assembly and the track pivot whereby the reaction forces of the pump produces a total reaction force biased about the pintle and displaced angularly from the track pivot, the major component thereof being carried by the track pivot while direction of total reaction between said assembly and said track ring to produce a minor component having a moment about said second axis,V

and a bowed resilient strut having substantially no rate placed in compression between said casing and said track ring, the ends of said strut being placed in a plane angularly displaced from a plane extending through said axes to produce a moment about said second axis in the same plane of but in opposition to the moment about said second axis produced by said minor component, said valve means being adjusted relative to the casing to vary the magnitude of the minor component.

13'.' A pump according to claim 12, in which said valve means and said assembly have cooperating ported surfaces which are surfaces of revolution about said rstv axis and are adjust,q

able relative to each other to vary the magnitude of the minor component.

14. A pump according to claim 12 in which said valve element comprises the spindle, upon Which-said cylinder assembly is rotatable, the land areas thereof being displaced angularly with respect to the plane extending through the axes.

15. A pump according to claim 12 in which the strut is bowed in initial compression to exert a predetermined force by location between end stops.

16. A radial pump of the kind specified, comprising a cylinder and piston assembly arranged for rotation upon a first axis, a track ring engaged by bearing means operating between said pistons and said track ring and movable upon a second axis in a constrained path in the direction of the plane of rotation of said assembly to vary its eccentricity relative to said assembly so as to Vary the stroke of the piston, a bowed resilient strut mounted in compression between said track ring and a stationary abutment of the piston and movable in the same plane as said track ring for urging said track ring to the eccentric position thereof, and valve means cooperatively related with said cylinder assembly and disposed with respect to said cylinder assembly and with respect to said track ring axis to produce rotational bias within said cylinder assem bly such that the direction of total reaction on said track ring produces'a component of force in the direction of said path which opposes said strut to move said track ring about its axisto neutral position thereof.

17. A radial pump as claimed in claim 16, in) which said valve means is so disposed that said component of force is a minor component of the total reaction.

18. A radial pump of the kind specified, comprising a cylinder assembly arranged for rotation about a first axis, a track ring pivotally supported for angular movement about a second axis substantially parallel with the: rst axis to vary the stroke of pistons of said assembly by variation of eccentricity, and valve means cooperating with said assembly and determining the direction of total reaction on said track ring so that a component of said reaction has a moment about said second axis, operating against resilient means to urge said track ring to maximum eccentricity setting, said first and second axes being so spaced that the center of the track ring moves in an arc about said second axis, which arc is selected to permit slight eccentricity of said track ring with respect to the rst axis at au times.

19. A radial pump of the kind specified comprising a cylinder and piston assembly arranged for rotation about a iirst axis, bearing means associated with the pistons, a track ring engaging said bearing means and vpivotally supported for angular movement about a second axis substantially parallel with the rst axis to vary the stroke of the pistons of said assembly by variation of eccentricity, resilient means operating between a fixed anchorage in the pump and the track ring to urge the latter towards full stroke position, and valve means constituting said rst axis having a high pressure port means cooperating with said assembly for determining the direction of total reaction on said track ring when the pump is operating against pressure, said port means being positioned with respect to said second axis to produce a component which is a substantially constant fraction of said reaction and having a moment about said second axis for moving said track ring against the action of said resilient means to substantially neutral position, which moment is substantially unaffected by the amount of eccentricity of said track ring, the high pressure port being so disposed that a line through the center of the valve and the center of the high pressure port is oil'set from the second axis.

20. A pump according to claim 19 in which said rst and second axes are so spaced that the centre of the track ring moves in an arc about said second axis which arc maintains slight eccentricity of said track ring with respect to the rst axis when in neutral position.

21. +A radial pump comprising a casing, a track ring pivotally mounted within said casing, a cylinder assembly including'pistons therein rotatable within said track ring about a fixed pintle, bearing means cooperating between said pistons and said track ring, a resilient strut under compression between said track ring and said casing in substantially parallel relationship with the periphery of said track ring to urge said track ring to eccentric position with respect to said cylinder assembly, said pintle having radial inlet and outlet ports therein of which outlet port is angularly offset forwardly in the direction of rotation of the cylinder assembly from a `perpendicular to the line joining the center of .track ring eccentricity, the said track ring being mounted for angular movement about a second axis parallel to and spaced from said first axis.`

HAMILTON NEIL WYLIE. 

